The gameplay is incredibly simple. You just move around (WASD, mouse) and collect orbs. Every time you get an orb, though, the speed of light slows down, so when you start moving, you're moving closer to the speed of light, and therefore closer to the qualities of special relativity. Some of these qualities include:

Red/blue shift: The world turns into this surreal rainbow whenever you're moving. At high enough speeds, if you look behind you, there's this deep blackness, because you're moving away from the light faster than the light can catch up to you. It scared the crap out of me when I first noticed it.

Lorentz Transformation: the distance between you and other stuff changes when you're moving close to the speed of light. I don't really understand what was going on with this, but it becomes more difficult to navigate.

Expanded visual range: When you're moving fast enough, you start to see different kinds of light. The stuff ahead of you looks bluer than it really is, but the creatures walking around look bright red, because they're giving off infra-red light.